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Industry News

Title : Solid-state Relays Technical FAQs


A Solid State Relay (SSR) is a totally electronic device that depends on the electrical, magnetic and optical properties of semiconductors to control the flow of current in a circuit. SSRs are an alternative to Electro-mechanical relays offering enhanced electrical performance and reliability. The main characteristic of a Solid State Relay is that it has no moving mechanical parts, which translates into a much higher life expectancy, among other benefits.

Solid State Relays have several benefits against their electromechanical counterparts. The following are only a few of them:

  • Extremely Long Life

  • Silent Operation

  • No Moving Parts Eliminates Arcing & Switch Bounce

  • Resistant to Shock and Vibration

  • Reliable Operation in Harsh Environments

  • Operation is Not Dependent Upon Orientation

  • Low Input Power Consumption

  • Reduced Electromagnetic Interference

When selecting a Solid State Relay several aspects must be taken into consideration, such as:

  • Load Voltage

  • Load Current

  • Input Voltage

  • Ambient Temperature

  • Mounting Style (PCB, Plug-in, Panel or DIN Rail mounting)

  • International Approvals (UL, CSA, VDE, TUV, etc.)

SSRs offer a high reliability alternative to electro-mechanical relays when switching a wide range of loads such as motors, heaters, solenoids, lamps, compressors, fans, among others, in applications as diverse as:

  • Coffee machines

  • Commercial / Industrial cooking equipment

  • Packaging machinery

  • Plastic machinery (extrusion/thermoforming)

  • HVAC & R systems

  • Lighting control systems

  • Lifts and escalators

  • Medical equipment

Unlike a typical electromechanical relay, there are several variables that will directly impact the life expectancy of a solid state relay in a given application. These variables primarily revolve around the electrical characteristics of the application, but some mechanical issues also impact the relay's life expectancy.

To assist with evaluating the reliability of their Solid State Relays, Crydom commissioned an independent specialized company to analyze the designs of several different Crydom SSR models. The final result yielded a MTBF rating of between 5 million and 34 million hours, depending upon the product family.

The following are some recommendation for the 4 pin header connectors that can be used with our Dual and Quad SSR’s with .025” square input pins:

  • Amp: Celduc Double Solid State Relay SCB965600

              Celduc Two Phase SSR - SOB965660    

                  Celduc  Quad Power SSR SCQ842060

                  Teledyne  Quad Power SSR SQ24D25